Composite tubular structure



p .39- w. s. YATES 2,172,429 2 COMPOSITE TUBULAR STRUCTURE Filed Aug. 29, 1956 patented Sept. 1939 area stares assent series araaaea CODEPPSITE TUBULAR $TREIQTURE This invention relates to metallic structures and methods oi fabricating them, and particularly to composite tubular structures.

An object of the invention is to provide simple,

is easily made composite tubular structures consisting of two or more metals of different characteristics each of which endows the structures with predetermined desired qualities.

A further object of the invention is to teach 10 convenient method through the practice of which the composite tubular structures may be produced.

As is well known, metal tubes and tubing are widely used for ornamental purposes and for id utilitarian purposes not related to the conduction of fluids. For example, metal tubes and tubing are used for hand rails, hand grips, and guard rails in architectural structures, as on stairways, and in public conveyances such as 20 railway coaches, motor coaches, and street railway cars. They are used in the construction of fixtures, particularly for the support of articles to be moved by sliding, as in tray supports associated with the counters of cafeterias, and as 25 foot rests and foot rails. Tubing is being used extensively in the manufacture of frames for certain articles of furniture, such as chairs and settees, and in the frames of seats of railway and motor coaches.

30 In all of the above uses of metal tubes and tubing it is the nearly universal custom to provide a smooth, highly reflecting external surface, not only to present a pleasing ornamental appearance, but also to facilitate cleaning and 35 the maintenance of a reasonable degree of sterility, having reference to accumulations of bacteria and disease germs deposited principally by human hands.

An optimum freedom from surface oxidation 4a or other corrosion is also highly desirable, as

frequent scourings are required to combat rapid corrosion, and in addition, corroded surface accelerate the accumulation of bacteria and disgenerally corrosivecharacter, or fluids that must be kept substantially free from contamination of any sort, are to be flowed through the tubing. Fluid substances intended for human use or consumption are among the last mentioned types of 5 Heretofore, metal tubes most widely used for utilitarian as well as ornamental purposes, and the exposed surfaces of which were capable of being kept reasonably clean and sanitary, owed thesedesirable properties not directly to any characteristics of the metal of which the tube was fabricated, but to treatment of the surface in various ways, among the more common of which were the application of thin films of such metals as nickel, chromium, or cadmium, by processes of electrodeposition. The processes by which such metals were applied to tubes were relatively costly, and frequently the coatings peeled or flaked ed and were not particularly g resistant to corrosion. Another undesirable characteristic of the plated tubes was that they were susceptible of marring, such as by scratching or breaking of the electrodeposited coating. Tubes having the surfaces treated 'as outlined above were used because of the lack of better products, although in many instances they were admittedly far short of ideal.

Among the alloys recently developed and brought into commercial use are certain ferrous alloys that contain carbon and substantial percentages of chromium,'and in some instances various percentages of other metals, and that are designated as steel, and in particularly are identified by the adjective stainless. These chromium. steel alloys are characterized by great resistivity to corrosion and the capability of being burnished to a high luster which they retain for a long period of time. Dirt does not cling to smooth surfaces of such alloys and they 40 disintegrate nor otherwise contaminate fluids which must be kept'in a high state of purity,

such as substancesv intended for human use or consumption.

The hereinbefore described chromium ste alloys have not come into widespread commercial I use in the manufacture of tubes and tubing for ornamental and utilitarian 'use as rails, handgrips, and posts, nor for the conduction of fluids even though they possess the ornamental and stain resisting properties most suited to such uses. -The principal reasons for this situation are that these alloys, in sufficient metal thicknesses to constitute rigid, durable, self-sustain ing tubes, are very difficult to work, and the tubes which have been produced are so costly as to prohibit their use in quantities. Accordingly, a large'field of uses to which the properties of the corrosion-resistant chromium steel alloys are particularly suited have heretofore been and are now being deprived of these materials.

Other alloys which exhibit properties of high resistivity to corrosion and the ability to acquire and retain a luster, or other desired characteristics, may be employed instead of the chromium.

I More specifically, the invention contemplates a thin-walled tube formed of sheet material having its edges oppositely reversely bent and interengaged in folded form to provide a seam lock, surrounding or surrounded by, as the cy be, atube ofthicker, and in all probability baser sheet metal, the edges of which are spaced apart so as to abut and thus confine the seam lock of the thinner tube. In order that the seam lock may enter the space between the edges of the sheet of which the thick-walled tube is formed. the seam lock of an external thin-walled tube is formed interiorly thereof, and the seam lock of an internal thin-walled tube is formed exteriorly thereof.

The invention contemplates not only the composite tubular structures'described brie'fiy above, but also certain convenient methods through the practice of which the tubes may be produced." For a full and complete understanding of the invention, reference may be had to the following detaileddescription, taken in connection with the accompanying drawing in which Figs. 1 and 2 are sectional views showing partiallycompleted tubes in accordance with one embodiment of the invention in different stages of fabrication;

Fig. 3 is a sectional view showing a completed tube according to one embodiment of the invention Figs. 4 to '9 inclusive are sectional views showing partially completed tubes which, by difierent methods 'of treatment, are convertible into com-,

pleted tubes in accordance with Fig. 3; and

Figs. 10 and 11 are sectional views showing additional embodiments of the invention.

Referring now to the drawing, in which like.

reference numerals designate corresponding parts .throughout the several views, and particularly to Figs. 1 to 3 inclusive, the reference numeral it indicates a relatively thin-walled tube which may be. fabricated of a chromium steel alloy or other material having desired surface properties in-. cluding high resistance to corrosion and the ability to be burnished to a durable luster. may be produced from sheet material by any of several processes, one of which, for example, may be performed by the forming rolls of the well-known tube-forming rolling machine. Such a machine includes a plurality of sets of rotatable forming rolls, which, in several steps, may form sheet material into a cylindrical tube having the edges mutually inter-engaged and inter-folded to form the seam lock I'Iinteriorly of the tube ii.

'I'heseam lock i1 is formed by bending the edges of the sheet metal back upon themselves inwardly Tubeli.

and. outwardly, as shown at it and I9 respectively, and inter-engaging the reversely bent portions. The finished seam locked tube It has the portion 2| which is spaced leftwardly from the outward bend Iii extending outwardly in abutment with the inward bend'il, whereby the seam 22 is closed and a substantially smooth surface contour is provided at that point.

Into the tube is is introduced the relatively thick-walled open seam tube 23 which -is to serve as the strengthener or bodily support for the thin-walled tube I. The tube 23 may be formed of any easily worked and preferably inexpensive metal, suchas mild steel, and has the edges 25 of the sheet of which it is formed spaced apart a. distance as great as or. greater than the width of the seam lock i'l. When ready for insertion into the tube It, tube 23 is not completely cylindrical, but has an.upset portion 2i which presents a concavity 28 on the surface of tube '28. By means of the upset portion 2|,jtube 22, which in the completed tube is to closely aims and interiorly' support tube It, has alesser cross-section than tube It, whereby it may be inserted into tube It easily. After tube 2Ihasbeeninserted into tube fit, the "former may be expanded by a suitable forming operation to shape it into the ultimately desired form, which is substantially cylindrical.- This may be accomplished in several ways, such as, for example, by drawing a forming plug or a series of forming plugs through tube 23, meanwhile confining tube It or successive portions thereof in a sizing die, if necessary.

tenance of tube "in cylindrical form and of the desired diameter.

'Fig. 2 shows the composite tubular structure of the invention after the shaping of tube 23 has been partially completed. It will be noted that Theuse of the sizingdieinsures continued mainupset portion 24 has been worked so' that very ii tube 22 has been dimensioned to exert pressurewhen finally shaped. Thus the seam lock I1 is engaged, confined, and positively retained locked by tube 23. It-will be noted that in the embodiment shown in Fig. 3, internal tube 23 afiords no support in a. radial direction for that portion of external tube I! where seam lock'l'I is'formed, although in a modification to be described later.

support is provided for seam lock l'l. I'or ordi- 15' nary uses, the extra thicknesses of metal provided by the seam loci; should render that portion of tube it entirely self-supporting.

In the completed tube, seam. 22 is incapable of opening during use, due to. the confining action of tube 23, and in these uses in which the presence of seam 22 is not undesirable, the final structure may be as shown in Fig. 3, with seam 22 giving the appearance of a narrow, shallow groove along the surface oi'tube it. If, however, an appearance of seamlessness is desired, seam 22 may be filled and closed by the application of such processes as brazing, soldering, or welding.

In Fig. 4 is shown a tube I 6 similar in all respects to the external tubes of Figs. 1, 2, and 3, into which has been fitted an internal tube 3|. Tube 3| has no concave portion, as in the ease of tube 23, but is, instead, somewhat helical in crosssection, one of its edges 32, which correspond to edges 25 of tube 23, overlapping the other, whereby tube 3i may be easily inserted into tube iii. The structure shown in Fig. 4 may be converted into one identical with that shown in Fig. 3, by shaping tube M, such as by means of a forming plug, to expand tube 3! and shift inner edge 32 leftwardly and outwardly until it is brought into final position abutting the left side of seam lock it", as indicated in dotted lines. Inner edge 32 may be rounded outwardly to enable it to pass the inner left edge of seam lock i'l.

Fig. 5 shows a tube l6 having a seam lock ll and having fitted thereto an internal tube 33.

The latter tube is completely convex in crosssectional contour, but has the portion adjacent the edges 3&1 formed on sharply decreasing radii. Edges 3 3 are thus brought much closer together than the width of scam loci; it. The contour of tube 33, although differing from those of tubes 23 and 8!, enables tube 3% to enter tube i5 loosely. Thereafter, tube 33 may be expanded and reshaped to bring the surface thereof into complete engagement with the inside of tube it: and edges 3t into abutting or compressing engagement with the opposite sides of seam lock l'i. It will be noted that edges 3% are rounded outwardly to enable them to pass the inner edges of scam look 5? without deforming the lock.

Fig. 6 shows thin-walled tube It having, as in the case of the previously described structures,

internal seam lock i i. This tube has fitted thereto internal, relatively thick-walled tube 56 which is contoured for easy entrance into tube 85 on the same general principle as tube 23 in Fig. 1, except that whereas tube 23 has the single indented portion 245, tube 35 has a plurality of indented portions 3i, each of which constitutes a lesser deviation from cylindrical contour than does indentation 25 in tube 23. A forming plug or a series oi such plugs may be drawn through the assembly of tubes as and it to bring it through the stage indicated in dotted lines at 38, and finally to the contour shown in dotted lines indicated at 39, and identical with the structure shown in Fig. 3.

Fig. 7 shows a previously mentioned tube structure in which the internal tube furnishes support for the seam look as well as for the remainder of the thin-walled tube. As in the heretofore described structures, the outer tube is the tube [6 with the internal seam lock H. The internal tube, shown in dotted lines in the condition in which it is introduced into tube i6 and in full lines in the finished condition in order to show clearly the mannertn which seam lock I1 is reenforced, is indicated 4! The free edges 62 of the internal tube II are provided with flanges 48 coextensive tion against the inner face of seam lock i1. With this arrangement, the seam lock is confined and supported on all three sides thereof, and the resulting structure is more rigid than those previously described.

Figs. 8 and 9 relate to a single embodiment of the invention, in which the final structure is substantially identical with that of Fig. 3, as indicated in dotted lines in Fig. 9, but in which the method of producing the final structure is different in that the internal tube is fitted to an incompletely processed outer, thin-walled tube.

As pointed out in connection with the-description of Fig. l, a finished tube with an internal seam lock has the portion adjacent to the outwardlv bent edge extending outwardly in abutment with the bend of the inwardly bent edge. The portion referred to is designated in Fig. 1 by reference numeral 2|. Before the operation of bending thisportion outwardly is performed, there is no complete seam lock, but merely an interengagement of the oppositely bent edges, as indicated at 46 in the outer tube 61 shown in Fig. 8. The tube 41 is not cylindrical in the condition shown in Fig. 8, as one portion 48 of the wall of tube 41 is displaced from the adjacent portion 48.

Into the tube 41 is inserted the relatively thickwalled reenforcing tube 5| which has acrosssectioi'ial contour similar to that of tube 3| of Fig. 4, which may be described as substantially helical. The free edge 52 is displaced inwardly from free edge 53, in order that tube 5! may enter tube 41 loosely, and for the additional reason that, tube 41 being non-cylindrical and the seam lock being incomplete, only the edge'53 can be placed in engagement with the completed portion thereof.

The solid line portion'of Fig. 9 shows the structure of Fig. 8 after a forming operation has been performed to carry the tube forming process forward to the extent that tube 5! snugly engages the interior of tube 41. There remains the operation of eliminating the offset between portions 48 formed by means of a forming plug which acts on that portion of tube 5| which terminates with edge 52 to bring that edge into alignment with edge 52, thus bringing portion 48 of tube 41 into alignment with portion 49 and completing the seam lock and the confinement of that element between edges 52 and 53, as well as perfecting the cylindrical contour of the structure, all as shown in dotted lines in Fig. 9.

' reenforcing engagement with the outer tube and in abutting relation with the seam lock. Thus, from thestandpoint of manufacturing technique,

and 49 of tube 41. This operation may be perand repeated' that a single forming plug or a an independent operation and the attendant handling are eliminated.

With reference to the shaping operations heretofore described, the statement has been made of a single forming plug, suitably-tapered and operations.

otherwise contoured, there may be eiiected the steady shaping of tube It from the contour shown in Fig. ltothatshowninl 'ig. 8, or the shapingoftubeilthrcughtheseveralstages shown in Fig. 6, or the of the structure of Fig. 8 to achieve the'structure shown in-dottad lines in Fig. 9. similarly the final structures represented in the other figures heretofore described may be achieved by continuous forming attentionisnowdirectedtol lg, 1 0,whereinis disclosed a tubular structure in which internal rather than externalgsurface characteristics are of primary concerni the thinwalled tube, fabricated fromthe chromiumsteel acterlstics, is the internal tube. a l-contrasted with previously described embodiments illustiatedintheiirstnine-iiguresofthedrawlng.

The referenoenumeral OI designates arelatively thin-walledtube having a seam lock it similartothose exteriorly of tube ll, whereby a substantially smooth cy "cal interioris aflorded bythe structureo tube at. Since the nature of the conveyance of fluids, it is probable that tube ti willbeusedforsuchpurposaandthereforeit isnecessary forthetubetobefluid tight. Tube ti maybe made leakproof by brazing, soldering. orwelding'throughout itslmgthalong thelocked external seam, indicated by the reference numeral CI. tight, it is inserted into arelatively thick-walled reenforcingtubeltwhichasinthecaseofthe internal reenforcing tubes shown in the previously described figures, may be of mild steel or anyothereasilyworhedmaterialwhichwillafford rigidity. Tube, may be formed from sheet with the free longitudinal edges ll spaced apart-and the spacing-betwem edges ll ispreferablysumcienttopermittube Ii to enter tubeltloosely. Aftertube OI hasb'eenfltted to tube It. the latter maybe sha a forming die, sizing die, ing device,.to bring tube gagement with tube tl,- l'l into abutting relation with external seam lock. Tube it thus reenforces fluid conductive tube ti and provides the necasary rigidity for it.-and

alsoconfines'seamlockllwhicmthoughebposed. provides its own reenforcement, due to the plural thicknesses of metal. v

Fig. llshowsamultipletubestmcture similar to that shown inlig. 10, except that it-includes walled" and "thick wall alloyorothermaterialailordinganydeslredchar-.

previously described, but formed 0 interior of a'tubular is of-little impor- 'tanceimlesssuchstructureistobeused forthe After tube ll'hasbeen made fluid the equivalent of the feature by which the structure shown in Fig; differs from that shown in 'Fig. 3. Thetube 6| havingexternal-seam lock 32 rendered fluid tight at It is shown in Fig. 11 and is identical with the correspondingly numbered tube in Fig. 10. Reenforcing tube ll differs from tube 86 in that adjacent to its longitudinal edges 88 it is provided with flanges 'II a which overlie and enclose-and protect seam lock i2,..when tube 8| has been shaped to engage the surface of tube ii, in much the same manner shapmon such radii as the nature of the metals.

employed will permit.

In -the foregoing description, the reenforcing tube has, in each instance, been described as having its free edges abutting the sides of the seam lock of the thin-walled tube. This is considered the preferredconstruction, but the seam lock is a suiiiciently permanent element that the thick-walled tube may. if desired, be dimensioned to engage the inner or outer surface of the thinvzalkled tube without actually engaging the seam It is to be understood that the tcrms'thin' asused herein are purely relative, and that the principal and reenforcing tubes may be proportioned as desired;

Since the invention primarilycontempiates that metallic materials havlng's'uch properties as will fhedesircdinthe'seam-lockedtubeswillbecostly by comparison with materials of which the reenforcing tubes may be made. and may be relatively dimcult to form if thick. it is considered probable that the seam-locked tube will be as thin, as practical considerations may dictate, and that the metallic body needed for rigidity will be supplied'by the open seam tube.

-The foregoing description of the assembly of the internal and tubes and the shaping of one within orsabout the other has been premised on the condition that the internal and external tubes are previously formed separately anda're fitted one to the other and'shaped and sized to the desired condition. It should be clearly understood that such preforming ofboth tuba intended for a' composite structure is not essential, but that the internal tubes may be preformed. and the external tubes formed around them from suitable sheets in such processing devices as presses or rolling machines, and such machine forming of the external tube around the internal may include the formation of the seam lock. By means of rolling machines, both tubes may, if desired, be fabricated simultaneously, in

their proper interiitting, relation, i'rom sheets.

having suitable characteristics and thicknesses. It should also be understood that the shaping of the assemblies'shown in the drawing,.or the fabrication of one tube from sheet material about or within a preformed tube, or the simultaneous shaping of two superposed sheets, may be accomplished'in adraw bench.

be produced. The invention contemplates tubular structures having any desired cross-sectional --contour,' such as oval. square, rectangular; t'ri- 1i angular, etc., may be produced by any of the methods described herein.

At an early point in the foregoing description, there was set forth the probable use of chromium steel alloys for the fabrication of seam-locked thin-walled tubes in order that they may have desired properties, such as resistance to corrosion and durable luster. Such alloys are by no means the only alloys exhibiting those properties, nor are those properties the only ones which may be desired. It should therefore be understood that many other a'lioys, ferrous or non- :Z'errous, and containing various metals or comhinations of metals, whereby various properties are exhibited, may be employed for the production of the sheets irom which the thin-walled tubes areiomed.

Although specific embodiments of the invention have been ahown in the drawing and deso scribed in the ation, and specific meth by which such embodiments may be achieved have been outlined, it will be understood that the invention is not limited to such embodiments and methods, but that it is capable of modification and substitution, as to structures and methods, within the scope of the appended'claim.

What is eiaimed is:

In a tubular structure, a relatively thin-wallmi tube fabricated irom sheet material and having the longitudinal edges oi said sheet interfolded to form a seam lock disposed exteriorly of said tube, and a relatively think-walled tube fabrinoted from sheet material and having the longitudinal edges of said sheet spaced apart, said thick-walled tube conforming in contour to said thin-walled tube, and disposed around the thinwalied tube exterlorly thereof in engagement with look.

edges abutting; sai seam I S. S. YATES. 20 

